The goal of this research proposal is to evaluate the impact of acute drug response on functional magnetic resonance imaging (fMRI) signal. Specifically, this study aims to evaluate the effects of the selective serotonin reuptake inhibitor (SSRI), citalopram, on neuronal activation elicited during an affective task using fMRI, and to evaluate the impact of a polymorphism in the promoter region of the serotonin transporter gene (5-HTTLPR) on task-related neuronal activation during citalopram administration. This double-blind placebo-controlled randomized crossover of intravenous (IV) citalopram and normal saline during two fMRI scans in sixteen healthy subjects will generate the first in vivo human data regarding the regional effects of an SSRI on affective task-related neuronal activation. We hypothesize that acute administration of IV citalopram will oppose the task-related increase in neuronal activity in the amygdala, as measured by fMRI, and that this opposition will be blunted in subjects that carry the s allele for the 5-HTTLPR. The purpose of this award is to provide the applicant with two years of support during her doctoral training, while she completes this research for her thesis.